When stopping the engine, it is desirable that the piston is caused to stop at a predetermined position that causes no valve overlap in which an intake valve and an exhaust valve are both opened. This is because when the engine is stopped in a state where valve overlap occurs, exhaust gases in an exhaust passage flow back into an intake passage via the exhaust valve and the intake valve during stoppage of the engine, which can result in degraded engine startability at the following start of the engine and increased exhaust emissions.
On the other hand, conventionally, as a control system for controlling the opening degree of a throttle valve during stoppage of the engine, one disclosed in Patent Literature 1 is known. In this control system, during stoppage of the engine, after an ignition switch is turned off, the throttle valve is controlled to predetermined respective opening degrees of full closing, full opening, and intermediate opening, in the mentioned order, and the opening degree of the throttle valve is learned based on the opening degrees thereof detected by a throttle position sensor during the full closing and the full opening of the throttle valve. Further, after the ignition switch is turned off, prior to the above-described full closing control, the throttle valve is held at a predetermined opening degree, whereby during the full closing control, negative pressure in an intake manifold is suppressed to prevent occurrence of untoward noise during the full open control after the full closing control.